Daylight factor: CIE uniform sky

Hi @chris and @mostapha

Just have a quick question. How can I create a CIE uniform sky in the LBT 1.4.0 version of the HB- Daylight Factor component? It has an input in the legacy version, but not in the new version.


Hey @berrakbalci ,

If you want to run a study with a uniform sky, it sounds like you’re actually trying to compute the fraction of the sky that a surface can see (multiplied by the transmittance of the windows if there are any). In the LBT plugin we call this Sky View and you can compute it with the HB Sky View component.

The only possible difference between Sky View and your special daylight factor is that sky view has no light bounces and I don’t know if that’s important for your case. If you really need something with light bounces, you can generate a CIE uniform sky and do a HB Point-In-Time Grid-Based study like so: (62.2 KB)

The results there are daylight factor with a uniform sky using a light bounce.


Hi @chris and @mostapha
I am running Daylight Factor analysis for a building in Italy.
Daylight Factor (DF) is defined as the ratio of the indoor daylight illuminance to outdoor illuminance under an unobstructed overcast sky. (DF = 100 * Ein / Eext)
Since the luminance of the standard CIE overcast sky changes with altitude, according to “UNI EN 17037 - Luce diurna negli edifici”, I need to define the Outside horizontal illuminance (Eext) at 19200 lux.
But there is no input in the LBT 1.4.0 version of the “HB Daylight Factor” component for that.
I would appreciate it if you could tell me how I can set sky or Outside illuminance for DF study. Or at least understand what is the default Outside illuminance that is considered in componant.

Thanks for your consideration.

Hey @FatemehMohseni ,

The distribution of light across the overcast sky does not change much with the illuminance used to derive it. Granted, it can be a little different if the illuminance is a whole order of magnitude but you can see this for yourself with the components: (32.2 KB)

So the illuminance used for the overcast sky isn’t really going to have much of an effect but, if you really must know the illuminance used in the Daylight Factor recipe, you can see that it is 10,000 lux and this is even written into the filename of the sky:

In any event, I personally would not worry about the difference and I loose much more sleep thinking about the radiance parameters that people use. But, if you’re really concerned about it, then just use a Point-In-Time Grid recipe with the HB Certain Illuminance sky.

Dear @chris
I really appreciate your respond. It was a great help.
Thanks for your consideration.

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